1. Field of the Disclosure
The disclosure refers to a sniffer leak detector comprising a detector with a quartz window, and in particular a sniffer leak detector that can do with a relatively simple detection means for the tracer gas.
2. Discussion of the Background Art
For leak testing containers and pipe systems, helium is typically used as the tracer gas, and the escape of helium is detected using mass-spectroscopic methods. For this purpose, the gas is ionized and the individual constituents of the gas or their fragments are then separated using a combination of electric and magnetic fields. After separation, the helium ions are detected using a detector and the signal is subsequently amplified and evaluated. Helium may also be detected by gas chromatographic methods, where, however, the detection sensitivity is lower.
During sniffer leak detection, a constant defined volume of gas is drawn through a sniffer conduit. Depending on the gas throughput through the sniffer conduit and the leakage rate of a helium leak (in leak tests, test specimens are filled with helium and closed), a certain tracer gas concentration occurs in the sniffed gas flow. A small portion of this sniffed gas mixture is introduced into the detection system (mass spectrometer) via a flow divider. For a successful separation of masses in the analyser unit, the pressure in the standard detection system must not exceed several 1×10−4 mbar. Thus, the helium partial pressure to be detected is merely 10−10 mbar for a helium concentration of 1 ppm.
Generating a total pressure on the order of 1×10−4 mbar requires the use of a turbomolecular pump. The use of such a pump is expensive and increases the susceptance to failure and the maintenance effort of the system. It is desirable to allow for the detection of a tracer gas under atmospheric conditions so that the turbo molecular pump and the flow divider can be omitted.
U.S. Pat. No. 6,277,177 B1 (Leybold Vakuum GmbH) and DE 100 31 882 A1 (Leybold Vakuum GmbH) describe detectors for helium or hydrogen that comprise a quartz window membrane closing a vacuum-tight housing. The quartz window membrane forms a selective passage for the gas to be detected. The tracer gas detector arranged in the housing is a gas pressure sensor reacting to the total pressure of the gas having entered the housing. Since the quartz membrane is gas selective, the gas pressure detector determines the pressure of the tracer gas in the housing. The pressure sensor arranged in the housing preferably is a Penning pressure sensor having two mutually spaced parallel cathode plates and an anode ring provided between the cathode plates. The electric circuit including the cathode plates and the anode ring includes a current measuring device for measuring the cathode or anode current. A magnetic field is generated by a permanent magnet situated outside the closed housing. Such a Penning detector has the advantage that it is much simpler and more economic than a sniffer leak detector comprising a mass spectrometer. In quartz window technology, the entire gas flow is directed past the detector. Also during operation, the pressure at the sensor may correspond to atmospheric pressure. Thus, the helium partial pressure is 10−3 mbar for a He concentration of 1 ppm, i.e. it is seven orders of magnitude higher than the pressure of the standard method. Separating helium and other gases is effected by means of a thin quartz membrane exclusively allowing helium to get into the detection volume.
It is the object of the disclosure to provide a sniffer leak detector that is of a simple and economic structure and has a high sensitivity.